The study of SMS, a rare disease, has resulted in a better understanding of a more common disorder, IDDM, and has allowed investigators to gain insights into the molecular mechanisms of autoimmunity. Many unanswered questions remain, such as the specific site of disease activity in SMS, both at the bedside (cortex, brain stem, or spinal cord) and at the bench (neuronal cytoplasma or synapse). The association of SMS with neoplastic disease and the development of autonomicdysfunction are not understood. The next decade may provide answers to these puzzling issues.